In a typical cellular network, also referred to as a wireless communication system, User Equipments (UEs), communicate via a Radio Access Network (RAN) to one or more core networks (CNs).
A UE is a mobile terminal by which a subscriber can access services offered by an operator's core network. The UEs may be for example communication devices such as mobile telephones, cellular telephones, laptops or tablet computers, sometimes referred to as surf plates, with wireless capability. The user UEs may be portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another mobile station or a server.
UEs are enabled to communicate wirelessly in the cellular network. The communication may be performed e.g. between two US s, between a UE and a regular telephone and/or between the UE and a server via the radio access network and possibly one or more CNs, comprised within the cellular network.
The cellular network covers a geographical area which is divided into cell areas. Each cell area is served by a Base Station (BS), or Radio Base Station (RBS), which sometimes may be referred to as e.g. “evolved NodeB”, “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used.
The BSs may be of different classes such as e.g. macro eNodeB, home eNodeB or pico BS, based on transmission power and thereby also on cell size.
A cell is the geographical area where radio coverage is provided by the BS at a BS site. One BS, situated on the BS site, may serve one or several cells. Further, each BS may support one or several communication technologies. The BSs communicate over the air interface operating on radio frequencies with the user equipments within range of the BSs.
In some radio access networks, several BSs may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural BSs connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), BS which may be referred to as eNodeBs or eNBs, may be directly connected to one or more core networks.
UMTS is a third generation, 3G, mobile communication system, which evolved from the second generation, 2G, mobile communication system GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for UEs. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
In the context of this disclosure, a base station or radio base station as described above will be referred to as a Base Station, BS. A User Equipment as described above will in this disclosure be referred to as user equipment or a UE.
The reference “DownLink” (DL) will be used for the transmission path from the BS to the UE. The reference “UpLink” (UL) will be used for the transmission path in the opposite direction i.e. from the UE to the BS.
Cellular communication networks evolve towards higher data rates, together with improved capacity and coverage. In 3GPP, standardization body technologies like GSM, HSPA, LTE and LTE-advanced have been and are currently developed.
Voice over LTE (VoLTE), and also other cellular technologies like GSM, is characterized by talk and silence periods, in an alternating fashion, with reference to 3GPP TS 26.093 chapter 5, and ETSI TS 126 093.
When a UE has speech samples or data to be transmitted to the other end, the speech samples or data are supplied to a buffer in the UE, and under control of the BS will be scheduled for transmission to the Access Network (AN) over the interface between the UE and the BS towards the receiving end via a CN, in a Voice over Internet Protocol (VoIP) packet.
During a talk period, referred to as the UE being in a TALK period status, Speech frames are generated every 20 ms, and provided to a UE's buffer, to be scheduled to be transmitted to the BS, in case the speech samples are generated at the UE.
During a silence period, referred to as the UE being in a SILENCE period status, Silence Descriptor (SID) frames, conveying information about the acoustic background noise are generated and provided to a UE's buffer, to be scheduled to be transmitted to the BS, in case the speech samples are generated at the UE, SID frames are generally generated every 160 ms. A SILENCE period status is also referred to as a “SID status”.
With the Adaptive Multi Rate (AMR) speech codec during Source Controlled Rate (SCR) operation, as applied within the VoLTE system according to the referred 3GPP and ETSI standards, the first SID frame arrives 20 ms after the last Speech frame, followed by next SID frame (SID update frame) after 60 ms and then SID frames arriving every 160 ms. Talk can be resumed at any frame after any SID frame.
A proper detection and distinction between speech and SID frames, received by the eNodeB is important for efficient resource utilization and reducing packet delay time. For a BS scheduler that uses service aware buffer estimation to predict UL data with minimum reliance on UE buffer status report, it becomes important to make a correct decision about UE speech activity. E.g. the allocation of radio resources to one UE should be scheduled by the BS to an optimum to the other competing UEs benefits in the same Access Network (AN) system.
With service aware buffer estimation, a UE in TALK period status, the UE is periodically given radio resources. For a UE in SILENCE period status these resources are less frequently provided to, or withdrawn for a period, the UE so that they can be more efficiently utilized for the AN system.
However, if these radio resources are withdrawn too early, such as in the case that the UE is still in TALK period status and thus has Speech frames to be transmitted, this withdraw will cause in packet delays.
On the other side if the radio resources are withdrawn too late, i.e. the UE is already considerable time in a SILENCE period status, the late withdraw results in resource wastage
Generally, a resource is allocated when the BS detects that the UE is in a TALK period status, and the resource is released when the BS detects that the UE is in a SILENCE period status. Erroneous detection by the BS of a of UE's TALK period status can lead to wastage of the network resources and UE battery consumption.
Erroneous UE's TALK period status detection will cause the BS scheduler using service aware buffer estimation to predict UL-data, will keep on granting the UE if it erroneously stays in TALK period status for transmissions with Speech frames. If the UE has already switched to SILENCE period status, this will cause the UE to send empty transmissions in UL. These empty transmissions will be meaningless and result in UE battery drainage.
Erroneously detecting a UE's SILENCE period status can cause packet delays to the receiving end while the BS scheduling for UL transmissions is less frequent, thereby deteriorating voice quality.
A prior art example that presents detection of a SILENCE period status in a UE is U.S. Pat. No. 8,509,108 B2 “Apparatus and method for detecting voice period in mobile communication system”.
This prior art example applies both packet size and inter-packet arrival interval to determine the UE's TALK- or SILENCE period status by Speech and SID frames received by the BS, based on an AMR codec deployed.
The prior art example determines the UE's status by comparing a maximum size of a SID frame and a minimum size of a Speech frame corresponding to determine a currently applied codec rate, and detecting the voice period by using any one of a packet size and an inter-packet interval according to the comparison result.
Problem with solutions based on packet size are e.g.:
Regarding a Voice codec rate: The voice codec has a variety of ranges, which will make the SID packet size to vary greatly. Moreover, for AMR codec, the codec rate can change during the conversation.
Regarding Robust Header Compression (RoHC): RoHC is a framework for compression of headers of Internet Protocol (IP) packets. The size of the headers of bearers carrying VoIP calls is compressed and thereby a voice call needs less bandwidth. The compressed size depends on the IP version used (IP version 4, IPv4 or IP version 6, IPv6). Hence RoHC can change the VoIP packet IP type sizes.
Regarding RTCP (Real-time Transport Control Protocol): VoIP media is carried by IP-User Datagram Protocol (UDP)-Real Time Protocol (RTP). RTP is a general purpose protocol used mainly for streaming multimedia applications. RTP is used in conjunction with the Real-time Transport Control Protocol (RTCP). While RTP carries the media streams (audio or video), RTCP monitor transmission statistics and quality of service information.
RTCP packets are different in size than RTP speech or SID frames. RTP and RTCP utilize the same Quality-of-service Class Identifier (QCI), so detection based on packet size becomes difficult.
Problem with solutions based on packet interval are e.g.:
Regarding RTCP: RTCP packets do not follow the structured inter-arrival pattern as RTP TALK/SID frames do.
Regarding Re-transmissions: Re-transmissions happen regularly on an air interface. These re-transmissions will change or at least influence the inter-arrival time between packets.
Regarding Segmentation: In addition to re-transmission, segmentation of packets will also cause delay in arrival of packets, and hence influence the interval timing.
Although reliable interval timing in a network with a fairly predictable air interface is a challenge, a system which is close to its full capacity with deteriorating radio conditions is even more a challenge to detect a UE's TALK/SILENCE period status when the BS scheduler cannot properly schedule the UE to a nominal scheme.